Apparatus for degassing molten metals



Aug. 24, 1965 s. FARRER APPARATUS FUR DEGASSING MOLTEN METALS 2 Sheets-Sheet 1 Filed June 8, 1962 Fri-2..

1955 s. FARRER 3,202,409

APPARATUS FOR DEGASSING MOLTEN METALS Filed June 8, 1962 2 Sheets-Sheet 2 FIG. 2.

United States Patent 3,2tl2,4ll9 APPARATUS FOR DEGASSENG MULTEN IVHETAL Sydney Farrel", Shea-held, England, assignor to The Bryan Donlrin ornpany Limited, hesteriield, England, a company of Great Britain Filed June 3, 1962, Ser. No. 261,116 Claims priority, application Great Britain, June '16, 1961, 21,918/61 '4 Qlaims. (Cl. ass-3e) This invention relates to the degassing of molten metals during casting thereof.

it is well known that various metals, particularly steel, are improved in quality if, when in the molten state, they are exposed to, or teemed in, a high degree of vacuum, say in the range or" /2 mm. to up to 20 of mercury absolute. For example, improvement in the quality of steels is achieved by teeming the molten steel into a chamher under vacuum conditions whereby the molten steel breaks up into and falls in the form of droplets; gases are thereby diil'used from the falling droplets and also from the body of molten steel which collects in the bottom of the vacuum chamber, the gases being exhausted from the chamber by the vacuum pumping system with which the chamber is provided.

In the case of steel, it is particularly useful to eliminate some finely divided solid material and several gases of which the most important is hydrogen, for which the vacuum type of treatment is particularly effective. The efficiency of the process depends on the degree of vacuum involved in the treatment, the size of the droplets which form when the steel is poured into the vacuum space, the time of the exposure of the metal to the vacuum and the amount of surface area of the collected metal exposed to the vacuum.

The traditional types of vacuum degassing equipment impose limitations in the methods of degassing molten metal in that most of them are capable of handling only batches of metal, i.e., the quantity which will fill a ladle which has to be removed from the vacuum chamber before casting is possible. Consequently, there is some cooling of the metal and some re-absorption of hydrogen from the air, and considerable time is involved in completing the process.

In one conventional process, a batch or ladle full of molten metal is degassed by inserting vacuum chamber inlet and outlet tubes in a tank of molten metal and having produced circulation of molten metal for a period of time, the molten metal in said ladle is then poured into ingots as required but this method also possesses the disadvantages mentioned above.

According to this invention, there is provided a procass for degassing molten metal which comprises establishing a mass of molten metal, teeming molten metal from said mass into a vacuum chamber whereby it falls freely in discrete droplets therein, intercepting the falling droplets by collecting them in a vessel Within and surrounded by the vacuum in said vacuum chamber whereby said collected droplets coalesce or reform in said vessel as a further mass of molten metal which has been subjected to preliminary degassification, teeming said further mass of molten metal from the vacuum surrounded vessel whereby it falls freely in discrete droplets to the bottom of the vacuum chamber to coalesce or reform into a stream or pool of finally degassed molten metal, and discharging the finally degassed molten metal from the bottom of the vacuum chamber through a barometric leg into an ingot mould or other container.

Preferably, the collected mass of preliminarily degassed molten metal in the vacuum surrounded vessel is teemed therefrom at the surface of said mass.

masses Patented Aug. 24, 1965 ice The operation of teeming of the molten metal from the vacuum surrounded vessel may be carried out meanwhile as teeming from a receiving container into the vacuum chamber proceeds once the latter teeming operation has commenced.

The falling droplets of molten metal from the vacuum surrounded vessel may be further intercepted and be given a final and guided cascaded movement before reaching the stream or pool of molten metal.

For carrying out the process of degassing molten metal according to the present invention there is provided an apparatus comprising a vacuum chamber, a molten metal-receiving container supported or adapted to be supported by the vacuum chamber in overhead and vacuum sealed relation thereto, a controlled teeming outlet in the receiving container for the flow of molten metal therefrom into the vacuum chamber, a tiltable vessel accommodated interiorly of said vacuum chamber for receiving the molten metal from said teeming outlet of the receiving container, pumping means connected to the vacuum chamber for obtaining vacuum conditions therein, means operable exteriorly of the vacuum chamber for tilting said vessel within said vacuum chamber, and a barometric leg communicating with the vacuum chamber for the discharge of molten metal therefrom.

The lower part of the vacuum chamber may be provided with a well or the floor of said chamber may have a fall leading to and constituting part of the upper end of the barometric leg.

The well or floor of the vacuum chamber may he stepped for imparting a cascading movement to the molten metal in flowing to the barometric leg.

The tiltahle vessel may conform to a ladle.

Water cooling circuits are also fitted to the exterior of the vacuum chamber near the jointing rings or otherwise as required.

The means for tilting the tiltable vessel or ladle may be hydraulically or pneumatically operated means.

The apparatus may be mounted on a trolley so as to be movable over a plurality of moulds or other containers for the casting of degassed molten metal thereinto one after another. Alternatively, the apparatus may be supported by a staging over a runway along which a trolley carrying a plurality of moulds is movable for bringing the moulds successively into position beneath the barometric leg.

A typical embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a sectional elevation of a vacuum degassing apparatus.

PEG. 2 is a sectional end elevation of same.

in the drawings it represents a refractory lined vacuum chamber and llll is a refractory lined molten metal receiving container removably supported on the roof of the vacuum chamber in vacuum sealed relation thereto and provided with a bottom teeming nozzle 12 in register with a molten metal inlet 13 and vacuum sealing plate 14 therein in the roof of the vacuum chamber 16, the teeming nozzle 12 in the container 11 being controlled by a stopper 15 in well known manner.

Disposed in the vacuum chamber ill beneath the inlet 13 thereof is a refractory lined ladle lit-3 provided with extended trunnions l7 rotatably mounted in bearings 18 in opposite walls of the chamber ill) whereby the ladle i6 is capable of being tilted about the common axis of its trunnions by means (not shown) fitted to one of the trunnions exteriorly of the chamber, said bearings and trunnions having water cooled vacuum seals 19.

The lower part of the vacuum chamber lid is provided with a stepped wall 2% beneath the ladle ltd while the floor 2,1 of said chamber is provided with a fall to form a well 22 leading to and forming part of the upper end of a barometric leg 23, the lower end of which is provided with a sealing unit 24 adapted to hold molten metal within said leg and the vacuum chamber until a balance is ob tained between the atmospheric pressure outside the chamber and the weight of metal inside the barometric leg 23 and said chamber.

A number of gas burners 25 extend through the Walls of the vacuum chamber 1% and vacuum pumping means (not shown) are connected to the vacuum chamber by way of a pipe 26 for obtaining vacuum conditions therein while a viewing port is provided in the wall of the vacuum chamber at 27. Water cooling circuits (not shown) are also fitted to the exterior of the vacuum chamber as required.

The vacuum chamber it) is supported by a staging 2:; over a runway 29 for a trolley 30 carrying a line of moulds 31 so that said moulds can be brought successively beneath the barometric leg 23. i

In carrying out the degassing of molten metal and casting of same into the moulds 31 with the apparatus shown in the drawings, said apparatus is first prepared by tilting the ladle 16 in the chamber over to an angle as indicated in chain lines in FIG. 1 and the burners 25 are fed with liquid or gaseous fuel and lighted so as to heat the heat-resistant refractory lined internal surfaces of the vacuum chamber and ladle therein.

A cold water supply is fed to all cooling circuits adjacent vacuum pressure gaskets and enclosed viewing ports.

When the refractory lining material exposed to the hot flame or gas from the burners 25 has reached a temperature such that a negligible amount only of heat will be taken up from the molten metal to be degassed to cause cooling thereof, the burners are switched off and the vacuum chamber made vacuum tight.

The vacuum pumping means, which may consist of steam ejectors, diffusion pumps or a series of Roots-Connersville type blowers and pumps arranged for vacuum pumping duty, are then started up and the pressure in the vacuum chamber reduced to the level of vacuum at which it is desired that the particular metal shall be processed. This pressure is normally in the range of /220 mm. of mercury absolute although much lower pressures and somewhat higher pressures may be used in certain circumstances.

A supply of the molten metal to be treated is then teemed into the receiving container 11 from a furnace ladle (not shown) and when suflicient mass of metal has accumulated in said container the stopper is lifted and the soft metal plate 14 below the teeming nozzle of said receiving container becomes fused by the molten metal therein which then falls into the vacuum chamber 10.

The molten metal, on entering the vacuum chamber, disperses in the form of discrete droplets which, being of small dimensions, provide ready escape of included hydrogen therein to the surfaces thereof so as to be diffused into the vacuum space. It is well known that the stream of tiny droplets diverge at a fairly large angle, probably 4050 from the teeming nozzle, and the position of the tiltable vacuum surrounded molten metal receiving ladle 16 in the vacuum chamber 1% is such that substantially all the droplets are collected in said ladle after they have given up gas during the time of falling, to coalesce as a further mass of molten metal which has undergone a preliminary degassification. When a sufficient quantity of such further mass of molten metal has accumulated in the ladle 16 as will fill the barometric leg 23 at the base of the vacuum chamber 10, said ladle is tilted and the molten metal teemed from the surface of said further mass passes through a second stage in which it breaks up into discrete droplets giving rise to further diffusion of included gases and is thereby finally degassed on reaching the barometric leg 23.

The degassed molten metal passing down the barometric pheric pressure outside the chamber and the weight of metal inside the barometric leg and the metal within the chamber after which said sealing unit is opened and molten metal in degassed condition allowed to discharge from the barometric leg in the mould 31 thereunder.

Molten metal continues to be received into the vacuum surrounded tiltable ladle 16 from the receiving container 11 so long as this is kept supplied by a furnace ladle or ladies and teeming from said ladle also continues to provide sufiicient head of metal in the barometric leg 23 and thus control the rate of outflow of degassed metal. If it is desired to interrupt the flow of molten metal from the barometric leg to enable a fresh mould 31 to be moved into position for the casting of a multiplicity of items, teeming from the ladle 16 within the vacuum chamber 10 is discontinued by tilting said ladle sufficiently back towards its upright position.

When casting a multiplicity of items, untreated molten metal continues to be fed into the receiving container 11 and into the vacuum chamber it? to collect in the vacuum surrounded ladle therein whether or not the latter is teeming or has been tilted back to temporarily discontinue teeming as required.

With apparatus according to this invention and operation thereof, the discharge of degassed metal from the barometric leg 23 can be independent of the rate of supply of untreated molten metal provided that adequate level thereof is maintained in the receiving container ll. Moreover, if the supply of untreated molten metal from any particular supply ladle is used up, then the process can continue independently, providing that a further supply of untreated molten metal becomes available before the receiving container 11 and the ladle 16 have been emptied.

Once the preliminary preparation stagesof pro-heating have been completed and teeming inaugurated, it is possible to continue the casting of degassed molten metal virtually continuously. This, of course, presumes that sufiicient untreated molten metal is available for processing and that suificient ingot moulds or other containers can be moved under the outflow end of the baro metric leg. The cost of processing per ton of metal is, therefore, relatively low on account of the large amount of molten metal which may be processed without shutting down of the plant and without the necessity for re-heating and pumping down.

With the process and apparatus according to this invention it is posible to stop and start the flow of processed metal so that a succession of moulds can be supplied irrespective of size, shape or capacity in terms of metal.

If the apparatus Were to be mounted on a movable platform, then any succession of moulds placed in line under the barometric leg could be filled without movement of the moulds themselves.

With this process there are two stages during which ditfusion of gas can take place from the falling droplets of molten metal within a single vacuum chamber, namely, first from the receiving container to the vacuum surrounded ladle and secondly from said ladle to the barometric leg. In this way, the time of exposure of the molten metal in discrete droplet form in vacuum conditions is considerably increased and the extent of difiusion of gases is also increased during degassification of molten metal within a single vacuum chamber.

Further, because the droplets are collected and thereby coalesced first in a vacuum surrounded vessel or ladle providing for a large surface area of molten metal therein which has been subjected to a preliminary degassification and then allowed to collect as a stream or pool of finally degassed molten metal providing another surface area thereof in the well or fall in the floor which forms part of the upper end of the barometric leg, a large surface area, in all, of the molten metal has consequently been exposed to vacuum relatively for a considerable time and diffusion will have taken place to a useful extent from those surfaces whilst the molten metal was exposed during the stages of teeming.

The use of the vacuum surrounded ladle adds to the storage capacity of the apparatus and thereby allows more time for continuous processing even though the supply of molten metal to the receiving container 11 from melting furnaces may be interrupted. Thus, with apparatus according to this invention, it would be possible to pour a very large ingot of degassed metal even though the untreated molten metal is supplied from several furnaces or by several furnace ladles of smaller capacity than the furnaces.

I claim:

1. In combination, a vacuum chamber; a container supported on said chamber for receiving a mass of molten metal; means for teeming molten metal from said container into said chamber whereby it falls freely in discrete droplets therein; a vacuum surrounded vessel within the vacuum chamber for intercepting said droplets which are thus collected in said vessel to coalesce as a further mass of molten metal; means for teeming said further mass from the vacuum surrounded vessel whereby it once again falls freely in discrete droplets to reform as a pool in the bottom of the vacuum chamber, said means comprising means for tilting said vacuum surrounded vessel; means for subjecting the molten metal to a cascading action before it reforms as a pool in the bottom of the vacuum chamber, said means comprising a stepped surface formed in the bottom of said chamber; and means for discharging the molten metal in the bottom of the vacuum chamber, said means comprising a barometric leg.

2. Apparatus for degassing molten metals having a molten metal-receiving vacuum chamber and an open top molten metal-receiving vessel mounted within said vacuum chamber, means for tilting said open top vessel within said chamber for spilling molten metal therefrom, a molten metal-receiving container removably accommodated on and in vacuum sealed relation to said vacuum chamber for teeming molten metal thereinto, and means including a barometric leg in the bottom of said chamber and a sealing unit at the discharge end of said barometric leg for supporting molten metal in said chamber.

3. Apparatus for degassing molten metals as claimed in claim 2, wherein the floor of the vacuum chamber is inclined downwardly leading to and constituting part of the upper end of the barometric leg.

4. Apparatus for degassing molten metals as claimed in claim 2, wherein the floor of the vacuum chamber has a stepped portion onto which molten metal is teemed from the tiltable vessel.

References Cited by the Examiner UNITED STATES PATENTS 2,054,922 9/ 3 6 Betterton. 2,882,570 4/59 Brennan 75-49 2,906,521 9/59 Harders 75-49 FOREIGN PATENTS 613,169 1/61 Canada. 833,925 4/60 Great Britain.

OTHER REFERENCES The Making, Shaping, and Treating of Steel, 7th Ed., published by US. Steel Corporation, Pittsburgh, Pa., 1957. Fold-out page following p. 334 relied upon.

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner. 

1. IN COMBINATION, A VACUUM CHAMBER; A CONTAINER SUPPORTED ON SAID CHAMBER FOR RECEIVING A MASS OF MOLTEN METAL; MEANS FOR TEEMING MOLTEN METAL FROM SAID CONTAINER INTO SAID CHAMBER WHEREBY IT ALLS FREELY IN DISCRETE DROPLETS THEREIN; A VACUUM SURROUNDED VESSEL WITHIN THE VACUUM CHAMBER FOR INTERCEPTING SAID DROPLETS WHICH ARE THUS COLLECTED IN SAID VESSEL TO COALESCE AS A FURTHER MASS OF MOLTEN METAL; MEANS FOR TEEMING SAID FURTHER MASS FROM THE VACUUM SURROUNDED VESSEL WHEREBY IT ONCE AGAINS FALLS FREELY IN DISCRETE DROPLETS TO REFORM AS A POOL IN THE BOTTOM OF THE VACUUM CHAMBER, SAID MEANS COMPRISING MEANS FOR TILTING SAID VACUUM SURROUNDED VESSEL; MEANS FOR SUBJECTING THE MOLTEN METAL TO A CASCADING ACTION BEFORE IT REFORMS AS A POOL IN THE BOTTOM OF THE 